Code Readiness: Laboratory Testing of Heat Pump Water Heater Performance: Impact of Airflow and Space Configurations

This research project was performed to support the development and implementation of California’s Title 24, Part 6 Building Energy Efficiency Standards (Title 24) by better understanding the impact of installation location and ventilation on consumer integrated heat pump water heaters (HPWH) performance. HPWHs are an all-electric water heating option that can achieve efficiencies three or more times greater than conventional electric resistance or combustion water heaters. To realize their highest efficiency levels, HPWHs require a sufficient thermal energy resource. Without ventilation guidance, building owners may end up installing HPWHs in small interior or exterior closets that lack adequate ventilation, leading to high electric resistance use, often during grid peak demand periods. 

This research project aimed to understand how room volume and ventilation impacts HPWH performance and to identify installation best practices for typical single- and multi-family HPWH installations. The research team conducted laboratory testing of three water heater products under different intake and exhaust ventilation configurations, ambient air temperature conditions, and room sizes to characterize HPWH performance under different installation situations. This report summarizes the technology background and study methods, discusses the lab test results, and outlines the demonstrated installation best practices and Title 24 enhancement recommendations.